1. Field of the Invention
This invention relates to curable epoxy resins having increased adhesive strength; and, more particularly, to certain amine cured epoxy resins containing certain polyether diureide additives.
2. Description of the Prior Art
Epoxy resins constitute a broad class of polymeric materials having a wide range of physical characteristics. The resins are characterized by epoxide groups which are cured by reaction with certain catalysts or curing agents to provide cured epoxy resin compositions with certain desirable properties. One such class of curing agents are generally the amines. The most commonly used amine curing agents are aliphatic amines such as diethylenetriamine, triethylenetetramine and the like and/or polyoxyalkylene polyamines; such as polyoxypropylenediamines and triamines.
Epoxy resin compositions having improved physical properties are obtained by employing polyoxyalkyleneamines, and polyoxyalkylenediamines in particular, as curing agents. It is common to employ with such expoxy resin compositions a co-curing agent such as those described in U.S. Pat. No. 3,549,592.
Also known to be effective as epoxy curing agents or co-curing agents are various ureas and substituted ureas, such as those disclosed in U.S. Pat. Nos. 3,294,749, 2,713,569, 3,386,956, 3,386,955, 2,855,372 and 3,639,338. The ureas disclosed in the above references are useful as either curing agents or as curing accelerators.
Aliphatic or aromatic compounds having a single terminal ureido group are well known. It has been disclosed in U.S. Pat. No. 2,145,242 to Arnold that diureido terminated aliphatic compounds can be produced by reacting an aliphatic diamine wherein each terminal amine has at least one labile hydrogen with urea. Other substituted ureas are disclosed in U.S. Pat. No. 3,965,072.
It has now been unexpectedly found that a specific diureide terminated polyoxyalkylene material having a molecular weight of from about 2000 to about 3000, when employed as an epoxy additive in combination with an aminopropyl ethylenediamine curing agent, provides cured epoxy resin compositions exhibiting outstanding strength of adhesion. Specifically, epoxy resins incorporating these additives, upon curing, provide a material with high tensile shear strength and superior adhesion to substrates. Use of the specific amine curing agents leads to strong adhesive bonds and avoids the problem of brittleness which arises when similar amine curing agents are used.